Structural characterisation of Ce0.5Zr0.5O2 modified by redox treatments and evaluation for chlorinated VOC oxidation

Abstract

In this work the application of a redox treatment consisting of a high-temperature reduction with 5%H2/Ar in the range 950–1075°C for 0.5–3h followed by mild oxidation at 550°C with 5%O2/He was evaluated as a tool for improving the catalytic performance of Ce0.5Zr0.5O2 mixed oxide in the combustion of chlorinated compounds. Structural, morphological and physico-chemical changes caused by the redox treatment were analysed by X-ray diffraction, Raman spectroscopy, BET measurements, NH3-temperature programmed desorption, temperature programmed reduction with hydrogen, and oxygen chemisorption. Interestingly, after reduction at a temperature as high as 1050°C during at least 1.5h, a substantially enhanced redox behaviour was noticed which resulted in a significant promotion of the catalytic activity in comparison with the unmodified parent sample. Hence, the value of temperature of half conversion at 30,000h−1 decreased from 300 to 275°C for the combustion of 1,2-dichloroethane, which was selected as a model chlorinated feed. This active performance was assigned to the formation of a new κ-CeZrO4 phase after redox aging characterised by a markedly increased capacity of providing active oxygen species at low temperatures. For comparative purposes two additional Ce0.5Zr0.5O2 samples calcined at 750 and 1000°C were also characterised and catalytically tested.